linux-kernel - Re: [PATCHv2] locking/atomics: build atomic headers as required

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Date:   Thu, 6 Dec 2018 17:13:44 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCHv2] locking/atomics: build atomic headers as required


* Mark Rutland <mark.rutland@....com> wrote:

> Andrew and Ingo report that the check-atomics.sh script is simply too
> slow to run for every kernel build, and it's impractical to make it
> faster without rewriting it in something other than shell.
> 
> Rather than committing the generated headers, let's regenerate these
> as-required, if we change the data or scripts used to generate the
> atomic headers, or when building from a pristine tree.
> 
> That ensures they're always up-to-date, allows them to be built in
> parallel, and avoid redundant rebuilds, which is a 2-8s saving per
> incremental build. Since the results are not committed, it's very
> obvious that they should not be modified directly. If we need to
> generate more headers in future, it's easy to extend Makefile.genheader
> to permit this.
> 
> I've verified that this works in the cases we previously had issues with
> (out-of-tree builds and where scripts have no execute permissions), and
> have tested these cases for both x86_64 and arm64.
> 
> The diffstat looks nice, at least...
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: linux-kernel@...r.kernel.org
> ---
>  Kbuild                                    |   18 +-
>  Makefile                                  |    8 +-
>  arch/arm64/include/asm/atomic.h           |    2 +-
>  arch/x86/include/asm/atomic.h             |    2 +-
>  include/asm-generic/atomic-instrumented.h | 1787 ----------------------
>  include/asm-generic/atomic-long.h         | 1012 -------------
>  include/linux/atomic-fallback.h           | 2294 -----------------------------
>  include/linux/atomic.h                    |    4 +-
>  scripts/Makefile.genheader                |   26 +
>  scripts/atomic/check-atomics.sh           |   19 -
>  10 files changed, 38 insertions(+), 5134 deletions(-)
>  delete mode 100644 include/asm-generic/atomic-instrumented.h
>  delete mode 100644 include/asm-generic/atomic-long.h
>  delete mode 100644 include/linux/atomic-fallback.h
>  create mode 100644 scripts/Makefile.genheader
>  delete mode 100755 scripts/atomic/check-atomics.sh

So these 'automatically generated' headers are actual and important code, 
and I think it's bad practice to remove these from the git grep search 
space and history as well.

Really, this whole notion of auto-generating the headers should be 
implemented correctly, instead of working around deficiencies in a 
short-term fashion that introduces other deficiencies.

I never got any replies to my previous comments about this:

  <20181128083057.GA7879@...il.com>

Did I miss some mails of yours perhaps?

Thanks,

	Ingo